In an airplane turbojet, for example, it is necessary to define and isolate an enclosure surrounding a mechanical member such as a bearing or a gear installed between two rotary shafts. Oil is injected into the enclosure to lubricate and to cool said mechanical member. Isolating the enclosure requires, in particular, a seal to be used between the two rotary shafts.
In that type of application, a distinction is made between seals that involve contact and those without contact. A seal with contact (a carbon gasket or a brush gasket) involves wear. It therefore needs to be changed periodically. In addition, the fragility of a carbon gasket can make it difficult to put into place. It is often also necessary to have a small flow of air entering the enclosure in order to maintain pressurization of the enclosure. Wear is even greater when the shafts are contra-rotating shafts.
A seal without contact, such as a labyrinth seal, requires air to be delivered at a much greater rate and it is sometimes difficult to obtain the desired pressure. In addition, an air and oil mixture is created inside the enclosure, which requires a de-oiling device before the air can be exhausted. The effectiveness of such a device is inversely proportional to the flow rate of air that it is to treat. It is therefore difficult to reach a compromise. Furthermore, a de-oiling device is expensive, bulky, and heavy.
The invention enables those various drawbacks to be overcome by proposing a seal structure, without delivering external air, and without wear that is harmful to the effectiveness of the system in the long term.